Article of manufacture containing hemp hurds



Patented Aug. 20, 1940 ATES UNITE. S

Martin J. Connolly, Danville, Ill.

No Drawing. Application July 11, 1935, Serial No. 30,946

6 Claims.

This invention relates to the preparation of cellulosic materials and more particularly to an improved method of producing a cellulosic materia1 in finely divided condition, particularly useful for incorporation in plastics as fillers.

As is known, large quantities of cellulose material are employed in the plastic industries as a filler. For example, the typical phenol formaldehyde resins, such as Bakelite, and the urea resins as marketed contain a relatively large percentage of a suitable filler, such as wood flour. The filler for such material should be of a proper color and, best to subserve its function, should not only be in finely divided form but should also be relatively granular. Heretofore the chief filling material for such plastics has been wood flour.

I have found that certain naturally occurring materials, and particularly hemp hurds, when subjected to a proper treatment, serve excellently as a filling medium for plastics, This material, when properly triturated or ground, classified and purified, presents all of the desirable characteristics demanded in plastic fillers and may be produced at a cost much less than the wood flour.

An object of the present invention therefore is to provide a new type of filler for molded plastics.

Another object is to develop a new plastic characterized by high strength combined with relatively low specific gravity.

Yet a further object is to provide a novel method for utilizing materials which have heretofore been Wasted for profitable commercial use.

With these and other equally important objects in view, the invention broadly comprehends the concept of utilizing cellulosic material of a naturally granular-like, as distinguished from a purely fibrous or flaccid, character as a filler for plastics and other analogous uses for which the peculiar physical characteristics of the material peculiarly adapts it.

The invention is more particularly concerned with the utilization of hemp but it will be understood that other starting materials of similar physical characteristics may be utilized.

Heretofore hemp has largely been profitably employed only in the production of relatively long fibers. For such use the hemp plant is harvested and then retted, the purpose being to strip off the external fibrous layer or screen. The retting process varies considerably, depending upon the particular use to which the material is to be put. Thus, for example, two broad steps or treatments have been employed in the past. The first of these consists of simple mechanical retting which comprises essentially subjecting the hemp stock to an abrupt or sharp impact for the purpose of fracturing or breaking the in- 5 ternal parenchyma or pith (known in the art as hurds) to thus facilitate the subsequent removal of the long external hemp fiber. Another general method employed is the so-called chemical retting. In this the plant is subjected to saturation with a chemical solution which serves to loosenup or degum the fibrous coating to thus facilitate its removal from the core.

As noted hereinbefore, the residual material, that is to say the central pith or parenchymatious material, has not been profitably employed in the industries. As intimated hereinbefore, I have found that this material after being subjected to a proper treatment, serves excellently as a filler for plastics.

In carrying out the invention the hemp is retted in any suitable manner, as for example by subjecting it to the action of a retting machine in such circumstances that the central core or pith is fractured and the external fibers are largely separated from the hurds. After separation of the long fibers from the hurds the hurds are then treated to reduce the particle size. Preferably this step is carried out in two stages. Thus in the preferred mode of operation the hurds, as recovered from the retting treatment, are subjected to a grinding or triturating action in a suitable mill, such as a hammer mill, so as to reduce the size down from about twenty-five mesh more or less to approximately fifty mesh. During this treatment, as will be appreciated, not only are the hurds broken up and reduced in size but the residual hemp fibers, which heretofore have adhered or clung to the hurds, are detached or freed. 40

Thereafter the mass is then subjected to a suitable type of treatment to remove the separated flaccid fibers. Preferably this is done by air classification and using any suitable type of air classifier, such for example as a Raymond classifier. As a result of this treatment the relatively light fibrous material is separated and removed from the hurds. The fibrous material thus treated may be subjected to any suitable type of treatment, such for example as treatment in acid or alkaline solutions for the purpose of making a high grade alpha cellulose or for any other purpose to which it may be put.

The preliminarily ground and classified hurds are then further reduced in size by remilling either in a hammer or ball mill, or any other suitable triturating machine, to bring the fineness down to the order of from fifty to one hundred mesh. It will be understood that the hurds, because of their brittle nature, lend themselves very readily to this type of grinding and such treatment, coupled with the air separation of the longer fibers, produces a very fine homogeneous filler. The finely divided hemp hurds as thus recovered may be employed directly as a filler in some of the cheaper colored plastics.

However, in order to improve the characteris tics of the material for this use it is preferred to give it a mild chemical treatment in order to bleach out and, if desired, chemically purify it. It is particularly to be observed, however, that the hemp hurds do not contain a very high percentage of ligneous material and hence the chemical or delignification treatment need be only of a mild character. As noted above, however, for some of the more expensive plastics it is desirable to improve the color of this material. This may readily be done by subjecting it to a suitable bleaching solution, such as a hypochlorite of suitable strength or a preliminary treatment with chlorine water followed by a hypo-- chlorite treat.

It is also to'be observed that in the process of making fillers from hemp hurds, if the ground material resulting from the first grinding is subjected to a screening, the hurds, peculiarly, segregate from the hemp fibers, the latter showing a remarkable tendency of gathering together or aggregating in nodules or lumps. Thus, according to the present invention, an intermediate screening step is contemplated. This may be carried out utilizing any suitable type of screen, such as a gyro-Sifter, and in these circumstances the material becomes practically self-cleaning, allowing a rapid and effective removal of the long fibers.

For some uses I have found that the seggregated long fibers may themselves be employed as a filler for plastics. In these circumstances the fibrous material is subjected to a grinding action either before or after a chemical treatment, when the latter is necessary to remove non-cellulos'ic material and bring up the color.

It has been found that operating according to the principles of the present invention an eminently cheap raw material, namely hemp hurds, may, with a simpletype of treatment, he made available as a filler for plastics. Due to its granular-like structure and low ligneous content it serves excellently in this field and requires a minimum of chemical treatment. Due to this low chemical cost, coupled with the cheapness of the raw material, it provides a'most economical product for this use.

As known to those skilled in the art, the filler may be incorporated in the plastic at any desired stage in the manufacture. That'is to say it is contemplated to incorporate the filler, in predetermined amounts, in the resin either in the beta stage or just prior to final hardening and molding.

While preferred embodiments of the invention have been described, it is to be understood that these are given merely to exemplify the underlying principles involved and are not considered to be definitive of the exclusive methods of preparing the new product.

I claim:

1. As an article of manufacture, a potentially reactive phenol methylene resin in which is homogeneously incorporated finely divided purified fibrous hemp hurds.

2. As an article of manufacture, a synthetic resin containing a filler, such filler comprising finely divided bleached fibrous hemp hurds.

3. As an article of manufacture, a synthetic resin containing a filler, such filler comprising finely divided purified fibrous hemp hurds substantially free from external hemp fibers.

4. As an article of manufacture a potentially reactive synthetic resin in which is incorporated a mixture of finely divided fibrous hemp fibers and hemp hurds.

5. As an article of manufacture a synthetic resin containing a cellulosic filler, such filler comprising ground fibrous hemp hurds.

6. As an article of manufacture, a synthetic resin containing a cellulosic filler, such filler comprising ground and bleached fibrous hemp hurds substantially free from hemp fiber.

MARTIN J. CONNOLLY. 

